1. Field of the Invention
The present invention relates to a ceramic electronic component and a manufacturing method thereof, and particularly relates to a structure and a forming method of an external terminal electrode provided in a ceramic electronic component.
2. Description of the Related Art
As a ceramic electronic component that is relevant to the present invention, for example, there is a laminated ceramic electronic component described in Japanese Unexamined Patent Application Publication No. 2001-267744. The laminated ceramic electronic component described in Japanese Unexamined Patent Application Publication No. 2001-267744 is also referred to as a multilayer ceramic substrate and includes a component main body having a laminated structure composed of a plurality of ceramic layers.
The multilayer ceramic substrate is mounted on a predetermined mounting board, and is provided with an external terminal electrode which is electrically connected to the mounting board. In general, the external terminal electrode of the multilayer ceramic substrate is formed by printing a conductive paste on a ceramic green sheet located at an outermost layer by means of screen printing, laminating the ceramic green sheet at the outermost layer together with other ceramic green sheets, pressing the ceramic green sheets, and then firing the ceramic green sheets. In addition, the fired external terminal electrode is subjected to nickel plating and gold plating or nickel plating and tin plating according to need in some cases.
However, when the external terminal electrode is formed by the above method, the following phenomena tend to occur.
In general, when the conductive paste is printed on the ceramic green sheet by means of screen printing, the conductive paste gathers at a center portion of a printed coating film due to surface tension of the conductive paste, and the thickness of the peripheral portion of the printed coating film is decreased.
In addition, the conductive paste adheres to and remains at the side surface of an opening in a transmission portion of a screen printing plate which transmission portion allows transmission of the conductive paste, and the thickness of the peripheral portion of a conductive paste film as the printed coating film is decreased.
Furthermore, in the pressing step, the conductive paste film is crushed in its thickness direction, and thus the conductive paste, in particular, the peripheral portion thereof, is decreased further.
As described above, when the thickness of the peripheral portion of the conductive paste film as the printed coating film is decreased, the thickness of the peripheral portion of the fired external terminal electrode is naturally decreased. However, stress that may cause peeling of the external terminal electrode is most likely to be applied to the peripheral portion. Thus, when the thickness of the peripheral portion of the external terminal electrode is decreased, the external terminal electrode easily peels off from the component main body, resulting in a problem that the bonding strength of the external terminal electrode is decreased. In addition, when plating is applied, a problem may also be caused that a plating solution infiltrates through the interface between the external terminal electrode and the component main body to further decrease the bonding strength.
As a measure to increase the thicknesses of the peripheral portion of the external terminal electrode, it is conceivable that printing of the conductive paste to form an external terminal electrode is repeatedly conducted, that is, the conductive paste is reapplied. However, when printing of the conductive paste is repeated by screen printing, as the thickness of the conductive paste film is increased, adhesiveness between the screen printing plate and the conductive paste film is deteriorated. Thus, the printability is deteriorated and the contour shape of the external terminal electrode is deteriorated. In addition, the repeated printing leads to a decrease of the productivity and an increase of the manufacturing cost.
Furthermore, in general, the conductive paste contains a sintering inhibitor such as alumina in order to increase a bonding strength with a ceramic material, and containing the sintering inhibitor increases a difference in shrinkage behavior between the external terminal electrode and the component main body in the firing step. Therefore, as the thickness of the external terminal electrode is increased, stress caused due to the above difference in shrinkage behavior is increased, and this stress may be applied to the component main body to cause undesirable deformation such as a warp and waviness in the component main body.
It should be noted that in addition to a laminated ceramic electronic component such as a multilayer ceramic substrate, the above problems may occur also in, for example, a ceramic electronic component having a non-laminated-type structure that includes a component main body composed of a single-layer ceramic substrate and in which an external terminal electrode is provided along a principal surface of the component main body.